The modest Irish movie has been transformed into a Broadway musical, but don't expect 'The Lion King.'

Reporting from New York — Actor Steve Kazee was leaving Broadway's Bernard Jacobs Theatre after a recent preview performance of "Once" when he was accosted by a woman who had just seen the show. Why didn't your character end up with the person he loved? the woman asked him. Couldn't he see they belonged together?

"She was saying it to me with some anger, as though I had personally made a wrong decision," Kazee said. "She felt so strongly that these were real people."

That ability to elicit an emotional reaction is the strength — and, producers hope, the saving grace — of "Once," a modest Irish movie that has made an unlikely odyssey from the Sundance Film Festival to a Broadway stage.

Most movies that wind up as Broadway musicals are splashy, blockbuster-derived productions, such as the long-running "The Lion King" or the upcoming "Ghost the Musical." "Once," which opens this weekend as one of the theater season's few new musicals, has followed a less-traveled path.

When it was released commercially five years ago, the micro-budgeted film charmed art-house audiences with its story of a down-on-his-luck Dublin busker, played by Glen Hansard of the Irish rock band the Frames and known in the film as Guy. On the cusp of giving up his music career, he is inspired to keep going by a blunt Czech immigrant (Marketa Irglova, known as Girl) who begins talking to him while he's playing on the street. The two initiate an awkward courtship that's centered on music (much of it written by Hansard) as his character turns his sad-sack life around. The pair also grapple with past relationships that they've clearly not put behind them.

But for all its sweetness, the movie was essentially just a minor hit. Hansard and Irglova, who became a real-life couple, had a fleeting moment of fame after their song "Falling Slowly" won an Oscar in 2008 and they formed the band the Swell Season. (The couple eventually broke up, a process documented in a later, even smaller film.)

The current theatrical production takes the offbeat story to a far grander place. After a run at a Cambridge, Mass., repertory theater and an off-Broadway house, this version, starring the relatively unknown Americans Kazee and Cristin Milioti, seeks to turn the film's wispy story into Broadway material.

Perhaps the most obvious difference between the film and the show lies with the music, with more traditional Irish foot-stomping numbers mixed in with "Falling Slowly" and the other acoustic folk songs. The show's music supervisor, Martin Lowe, said he wanted to bring a little more energy to the live production and offset some of the movie's melancholy notes.

Director John Tiffany admits he didn't immediately see "Once" as a stage production.

"When producers first came to me [in 2010] and said they wanted to make a show of this movie, I thought 'Wha'?!!" Tiffany recalled, as he sat in the basement of the theater before a performance. The actors were doing stretching exercises around him. "This isn't exactly 'Moulin Rouge.'" He paused. "But I like a challenge."

Enda Walsh, the Irish playwright whom producers approached, had an even more perplexed reaction. Known for penning dark stage dramas such as "Disco Pigs" and the intense IRA film "Hunger," Walsh immediately discarded the film script when it was sent to him. "This is a complete waste of my time,'" he remembered thinking.

But Walsh agreed to spend a few hours in London discussing the show with Tiffany and found himself coming around. "There was something about how positive its message was," Walsh said. "I knew there's not much of a story there, but there was something almost gorgeous about the idea of it, that someone can just come up and change your life, and then just like that they're gone."

Straddling the line between concert and drama, "Once" tries to capture the out-of-the-blue love story while fleshing out supporting characters (a barkeep, a banker). Milioti's Girl is more tart than Irglova's, with a fair share of punch lines. ("I'm always serious. I am Czech," she says, getting one of the bigger laughs of the play.) Milioti said she deliberately avoided seeing the movie before tackling the part so as not to be unduly influenced by it, and has had only minimal interaction with Irglova.

Like Milioti, most of the cast goes all the way back to the Cambridge production. Hansard helped the group with a workshop there, testing Kazee's musical chops while the two sat in, as Kazee recalled, a "10-by-10 room where he just said 'Go.'" He also contributed suggestions to the off-Broadway version. But Hansard has not been consulted heavily on the Broadway production or even seen it. John Carney, the director of the film "Once" and Hansard's former bandmate, has not been involved with it at all.